The present invention relates to height safety equipment and, in particular, to a fall arrest device used as a mobile anchorage to secure a user to an elongate support such as a cable lifeline. Such fall arrest devices are an important item of safety equipment for maintenance and construction personnel who work in high places, since they enable the hazards of falls to be minimised.
Some known fall arrest devices suffer from the drawback that they are incapable of negotiating the intermediate brackets along the elongate support element. One solution to this problem is to provide special brackets which can be xe2x80x9copenedxe2x80x9d to allow the user to pass. The weakness of this approach is that the elongate support element temporarily lacks support at the very point where the installer thought it necessary and at the precise moment when it is most needed. Another potential problem is that the brackets may not necessarily be accessible to the user.
Fall arrest devices have been developed which are capable of automatically traversing intermediate brackets for the elongate support element without user intervention. Such devices typically comprise a pair of rotatable wheels having a series of recesses at spaced locations around their peripheries, the adjacent recesses being separated by a radially projecting part of the wheel. A co-operating slipper part is mounted on the wheels by means of formations which inter-engage with complementary formations on the radially projecting wheel parts. A space between the slipper part and the wheels is dimensioned to receive the elongate support element, such as a cable lifeline.
European patent application number 0 272 782 discloses in a first embodiment a self-locking fall arrest device having a locking cam which is spring biased to a locking condition in which it firmly grips a safety line to lock the device to the safety line. In use, the device is connected to a lanyard of a personnel safety harness so that the loading applied to the locking cam by the lanyard is such as to maintain the locking cam in an unlocked condition, until such loading is released, for example in a fall arrest situation whereupon the locking cam is then pivoted by its biassing spring to its locking condition.
The above-described device is designed for use on vertical or near-vertical installations but has only unidirectional capability. This means that the device must be installed on the safety line or cable in the correct orientation for safe operation. Hence, the device is unsuitable for tasks which involve the user ascending one side of a tall structure and descending the other side. In order to make such a traverse safely, the user must detach the fall arrest device at the apex and re-orient it for the descent. Otherwise, the locking cam is on the wrong side of the device for effective deployment in a fall arrest situation.
In a further embodiment EP 0 272 782 discloses a second self-locking fall arrest device which is able to operate bi-directionally on vertical or near vertical installations. However, the device can only operate on safety lines at a greater angle to the horizontal than a critical angle.
Finally, in a third embodiment EP 0 272 782 describes a further self-locking fall arrest device comprising two self-locking fall arrest devices according to the first embodiment mounted back-to-back on an articulated chassis so that one of the self-locking devices will always be correctly oriented for operation regardless of the orientation of the safety line.
In practice, the requirement for a fall arrested device which has bi-directional capability in a vertical or near-vertical orientation is rare. It is seldom the case that workers ascend one vertical or near-vertical face of a structure and ascend a vertical or near-vertical face of the same structure using a common safety line spanning the two faces. It is much more likely that the respective faces will be equipped with individual safety lines. Hence, re-attachment of the fall arrest device in the correct orientation for the descent is not problematic.
However, the situation is different for personnel engaged in work on pitched rooves, for example, where a common lifeline may span both slopes. In the circumstances, it is irksome for the user to detach, re-orient and re-attach his fall arrest equipment each time he crosses the roof apex. In practice, many workers will not bother and may either leave themselves unattached to the lifeline or may choose to work at times with the fall arrest device incorrectly oriented for effective deployment. The latter option may lead workers to assume a false sense of security because they may become confused as to which side of the roof apex is the xe2x80x9csafexe2x80x9d slope.
It is therefore an object of the present invention to provide an improved fall arrest device having bidirectional capability for use on horizontal and inclined safety lines. It is a further object of the present invention to provide a fall arrest device which is capable of traversing intermediate support brackets for the safety line in hands-free manner, thereby enabling users to move about freely during execution of a variety of tasks without encumbrance. It is yet another object of the present invention to provide a fall arrest device having the capability to switch from one directional mode to another without user intervention, according to the change in slope of the user""s location.
The invention is a fall arrest device for use on an elongate support such as a safety line or a track, said device comprising:
a chassis having a safety retainer to retain the elongate support whilst allowing movement of the device therealong, and including an engaging element for slidably engaging said elongate support;
first and second locking cams for locking the device to said elongate support in a fall arrest situation;
a bias to urge one locking cam into locking engagement with the elongate support in response to a sudden change in load experienced by the device; and
an attachment for attaching a personnel safety connector to the device;
in which said first and second locking cams comprise first and second independent actuable cam elements respectively, and characterized by said cam elements being actuated by a common arrester in response to a sudden change in load experienced by the device such that said first cam element traps the elongate support between itself and said engaging element when the elongate support slopes in a first direction and such that said second cam element traps the elongate support between itself and said engaging element when the elongate support slopes in a second direction.
For the avoidance of doubt, it is hereby stated that the above references to the elongated support sloping in a first direction or sloping in a second direction means sloping in a sense having a positive gradient or a negative gradient. The meaning of the term xe2x80x9cpositive gradientxe2x80x9d is to be interpreted by reference to Cartesian co-ordinates as rising from left to right, whilst a xe2x80x9cnegative gradientxe2x80x9d is to be regarded as rising from right to left.
Preferably, the device includes at least one rotary member having at least one recess formed in its periphery, the rotary member being rotatably mounted in relation to said retainer. The recess is adapted to traverse an intermediate support used to support the elongate support, without the need for user manipulation, by rotation of the rotary member relative to the retainer such that elements of the intermediate support are successively received, guided and passed by the recess automatically.
In such embodiments, the rotary member may be a wheel having a plurality of petals projecting radially from a hub of the wheel, said petals defining between adjacent pairs thereof recesses for traversing safety line intermediate supports. An example of a device having this traversing capability is described in the applicant""s European patent application number 0 782 469, the disclosure of which is incorporated herein by reference.
The retaining means may include at least one slipper element for slidably engaging the elongate support and may co-operate with the wheel such that the wheel can rotate with respect to the slipper element whilst traversing the elongate support.
In addition, the device may be designed for easy attachment to and removal from the elongate support by making the components of the retainer movable relative to each other in such a way that a passageway may be created to allow access of the elongate support. An example of the fall arrest device having such removal/attachment capability is described in the applicant""s co-pending European patent application number 0 752 899, the disclosure of which is incorporated herein by reference.
The common arrester may comprise an arrester arm or a pair of arrester arms pivoted to the chassis and an arrester pin forming an axle for the locking cams, the arrangement being such that the arrester pin obstructs the pivotal movement of the arrester arm or arms in a fall arrest situation. Preferably, the arrester arm or arrester arm pair is alleviated above the arrester pin during normal use so that, in a fall arrest situation, the arrester arm or arrester arm pair is suddenly pulled downwards into contact with the arrester pin. It is the thrust exerted by such engagement with the arrester pin that causes locking engagement of one of the cam elements with the elongate support.
In an especially preferred form of the device, the locking cam elements are mounted at the ends of the cam links which are pivotally mounted on respective arrester arms. The pivot points are preferably formed as knuckles which serve as guides keeping the device in correct alignment with the elongate support. The knuckles may include torsion springs which, during normal operation, hold the cam profiles away from the elongate support. The action of these torsion springs also maintains contact between the knuckles and the elongate support. This includes a frictional resistance to sliding, thereby ensuring that, in the event of a fall, the victim falls faster than the device. In this way, actuation to fall arrest mode is quicker.
Preferably, the device includes a manually-operable switch to enable it to be reconfigured for safe operation according to the direction of the slope on which the user is working. As indicated above, the arrester arm or arrester arm pair needs to be above the arrester pin for effective operation of the device in a fall arrest situation. Therefore, when the user moves to a slope of opposite gradient, he needs to move the arrester arm or arrester arm pair past the arrester pin to the other side of the device. The manually-operable switch allows the arrester arm/arrester pin assembly to be moved relative to each other without the thrust engagement that would otherwise cause cam locking.
In an alternative arrangement, the switching can be arranged to occur automatically when the device passes through the horizontal between two slopes of opposite gradient. A gravity or pendulum switch is suitable for this arrangement. During normal use on a sloping surface, the gravity switch is incorrectly oriented relative to the arrester arm or arrester arm pair to allow accidental switching to occur. Likewise, during a fall arrest situation, the orientation of the switch relative to the arrester arm or arrester arm pair ensures that the arrester arm or arrester arm pair engages the arrester pin to effect cam locking.
Usually, the attachment for attaching personal safety means to the device is found at the opposite end of the arrester arm or arrester arm pair from its pivot point on the chassis means.